In this paper, we reflect
on three long-standing problems: The relationship between the physical world
and the perceived world, accounting for individual differences in the way in
which we perceive the world around us, and the problem of understanding other
minds. We begin by examining the relationship between synaesthesia and
hallucinations, as well as between hallucinations and normal percep­tion,
attempting to show in both cases that the phenomena in question may share more
in common than previously assumed. We consider the plausibility of a functional
analysis of synaesthesia and examine the mechanisms of the different types of
ordi­nary and extraordinary perceptions. We propose that synaesthesia-like
mechanisms may underlie a range of perceptual phenomena and cognitive functions
and demon­strate the usefulness of such an approach given the ubiquity of
synaesthesia-like mental processes in human cognition.